Polycarbonates are generally produced using bisphenols as monomer ingredients, and are in extensive use as engineering plastics in applications such as electrical/electronic parts and automotive parts and in the optical field including optical recording media and lenses, so as to take advantage of the superiority thereof in transparency, heat resistance, mechanical strength, etc. However, for application to optical compensation films for flat panel displays and the like, which are rapidly spreading recently, a higher degree of optical properties including low birefringence and a low photoelastic coefficient have come to be required. The existing aromatic polycarbonates have become unable to meet the requirement.
Conventional polycarbonates are generally produced from raw materials induced from oil resources. In recent years, however, there is a fear about the depletion of oil resources, and polycarbonates produced from raw materials obtained from biomass resources such as plants are desired to be supplied. In addition, since there also is a fear that global warming caused by an increase in carbon dioxide emission and accumulation thereof may bring about climate changes, there is a desire for the development of a polycarbonate which is produced using a plant-derived monomer as a starting material and is carbon-neutral even when discarded after being used.
A method in which isosorbide, which has a heterocyclic structure, is used as a plant-derived monomer to obtain a polycarbonate through transesterification with diphenyl carbonate has hitherto been proposed (see, for example, patent document 1). As a copolycarbonate produced from isosorbide and another dihydroxy compound, a polycarbonate obtained through copolymerization with bisphenol A has been proposed (see, for example, patent document 2). Furthermore, an attempt has been made to improve the stiffness characteristics of the homo-polycarbonate produced from isosorbide, by copolymerizing isosorbide and an aliphatic diol (see, for example, patent document 3).
On the other hand, many proposals have been made on polycarbonates obtained by polymerizing 1,4-cyclohexanedimethanol, which is an alicyclic dihydroxy compound (see, for example, patent documents 4 and 5). However, these polycarbonates have a molecular weight as low as about 4,000 at the most and, hence, many of these have a low glass transition temperature.
Polycarbonates produced from monomers having a heterocyclic structure, e.g., isosorbide, have high transparency, excellent heat resistance, a low refractive index, and a small Abbe number, and applications thereof are hence expected to spread to optical compensation films and the like. However, polycarbonates having such a structure are inferior in reactivity on one hand and have poor thermal stability on the other hand, as compared with the conventional aromatic polycarbonates including a bisphenol structure. When such a polycarbonate having a molecular weight required of molding materials is to be obtained by conventional production processes, performances such as color tone and transparency should be sacrificed. Furthermore, there has been a problem that thermal deterioration occurs during polymerization reaction to generate by-products including formic acid and this formic acid remains in the polymer and volatilizes during molding to arouse various troubles including corrosion of the mold and rolls.    Patent Document 1: British Patent No. 1079686, description    Patent Document 2: JP-A-56-55425    Patent Document 3: International Publication No. 2004/111106, pamphlet    Patent Document 4: JP-A-6-145336    Patent Document 5: JP-B-63-12896